Machine for grinding toothed parts



March 29, 1960 P. F. BARKER ETAL 2,930,163

MACHINE FOR GRINDING TOOTHED PARTS 9 Sheets-Sheet 1 Filed Sept. 6, 1957 FIG.|

ps ue IN VENT 0R5 PAUL F. BARKER March 29, 1960 Filed Sept. 6, 1957 P. F. BARKER EI'AL MACHINE FOR GRINDING TOOTHED PARTS 9 Sheets-Sheet 2 March 29, 1960 P. F. BARKER ETAL 2,93

MACHINE FOR GRINDING TOOTHED PARTS Filed Sept. 6, 1957 9 Sheets-Sheet 4 March 29, 1960 P. F. BARKER 2,930,153

MACHINE FOR GRINDING TQOTHED PARTS Filed Sept. 6, 1957 9 Sheets-Sheet 5 9 Sheets-Sheet 6 rim IN ERESS cou'rnol.

FF-ll P. F. BARKER EI'AL MACHINE FOR GRINDING TOOTHED PARTS I R-l 208 ZT-FQ March 29, 1960 Filed Sept. 6, 1957 OUT OUT

Fm OUT March 29, 1960 P. F. BARKER ETAL 2,930,163

' MACHINE FOR GRINDING TOOTHED PARTS Filed Sept. 6, 1957 9 Sheets-Sheet -7 MACHINE FOR GRINDING TOOTI-IED PARTS Paul F. Barker, Leonard 0. Carlson, William C. Critchley, and Nelson K. Haase, Rochester, N .Y., assignors to The Gleason Works, Rochester, N.Y., a corporation of New York Application September 6, 1957, Serial No. 682,380

19 Claims. (Cl. SI-32) The present invention relates to machines for grinding toothed parts, such, for example, as face toothed clutches.

Such machines have heretofore been arranged to automatically rough grind and then finish grind the teeth, and, in the course thereof, to automatically interrupt the grinding at suitable intervals and redress the grinding wheel. In both the rough and finish grinding phases there is a relative infeed between the grinding wheel and the workpiece to a predetermined depth, controlled by a variable depth stop, this infeed being followed by a relative withdrawal during which the workpiece is indexed'to bring another tooth space thereof into position for grinding. The alternate infeed and withdrawal is repeated until all of the teeth around the workpiece are ground. Then the variable depth stop is actuated so that during subsequent infeeds the teeth will be ground to a greater depth; and the cycle of infeed, withdrawal and indexing is repeated until all the teeth have been ground to the greater depth. Then again the variable depth stop is actuated to cause grinding to still greater depth, and so on. The sequence described continues through a number of operations of the variable depth stop which depends upon the amount of stock removed from the teeth during each grinding operation and the whole depth of the finished teeth. The sequence described has proven advantageous in that only a little stock is removed from each tooth at one time, so that burning of the teeth is avoided.

However, a considerable amount of time is consumed by the often repeated indexing, since before such indexing can take place the grinding wheel must be drawn entirely clear of the work, or vice versa, and, especially with massive workpieces, the actual indexing must be slow enough to keep acceleration loads on the indexing mechanism within practical limits.

The present invention is aimed at reducing the overall grinding time, and accomplishes this by eliminating most of the indexing operations during the rough grinding phase. Each tooth space is ground to full rough-ground depth before the workpiece is indexed to bring the next tooth space into position for rough grinding. However, for finish grinding, the conventional method is continued in the interests of obtaining maximum uniformity of the tooth surfaces and of tooth-to-tooth spacing. Burning of the teeth during the rough grinding is avoided by frequently separating the wheel from the work sufliciently to allow liquid coolant to enter between them.

A machine according to one aspect of the invention comprises a grinding wheel and a work spindle, means including a rotary feed cam for effecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a tooth surface of a workpiece on the spindle and for returning for a subsequent infeed, and means for angularly indexing the work spindle between successive infeed motions, the infeed portion of said cam comprising a plurality of discrete infeed sections separated by retraction sections,

United States atent "roe so that while the infeed is occurring the wheel and the tooth surface being ground are periodically separated- According to another aspect of the invention the machine comprises a grinding wheel and a work spindle, a feed cam for effecting alternate relative infeedand return motions between the wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle between successive infeed motions, said feed cam having a roughing feed path and a finishing feed path, means to render one or the other of said feed paths effective, a variable stop to limit the depth of grinding engagement between the grinding wheel and work on the work spindle, and means for holding said stop against advance while the roughing feed path is effective and for advancing said stop while the finishing feed path is eliective.

The foregoing and other aspects of the invention will appear from the following detailed description of the 7 preferred embodiments shown in the accompanying drawings, wherein: V

Fig. 1 is a plan view and Fig. 2 is a front elevation of the machine;

Fig. 3 is a fragmentary vertical section through the grinding wheel and the supporting structure and feed mechanism therefor;

Fig. 4 is a diagram showing the index mechanism for driving the work spindle;

Figs. 5 and 6 are diagrams to further illustrate the index mechanism and its mode of operation;

Fig. 7 is a diagram of the indexing cycle;

Fig. 8 is a diagram of the hydraulic system of the machine;

Fig. 9 is an elevation, partly in vertical section in plane 9-9 of Fig. 1, of the mechanism for controlling the motion and position of the work support relative to the machine frame;

Fig. 10 is a plan view of the feed cam and related switches;

Figs. 11 and 12 are schematic views showing other positions of the feed cam;

Fig. 13 is a diagram showing one way in which the machine may be wired electrically;

Fig. 14 is a fragmentary section in a plane corresponding to that of Fig. 3, illustrating a modified feed cam shifting mechanism;

Figs. 15 and 16 are schematic plan views respectively of the section of the feed cam shown in Fig. 14 that is eifective during rough grinding and of the section that is effective during finish grinding; and,

Figs. 17, 18 and 19 are respectively hydraulic, drive and electrical diagrams for the machine having the modified mechanism of Fig. 14.

'Referring to Figs; 1 and 2, the machine comprises a frame 20 on which a sliding base '21 is movable along horizontal ways 22. On base 21 a cross-slide 23 is adjustable horizontally, along ways 24 which are perpendicular to ways 22. Awork head 25 is adjustable angularly on the cross-slide about a vertical axis 26 and journals a work spindle 27 for rotation about a horizontal axis 28 which intersects vertical axis 26. The workpiece, in this case a face toothed clutch member C, is secured to the spindle by suitable chuck means. In many respects the machine corresponds to that described and claimed in [1.8. Patent No. 2,395,544 to C. T. Galloway. i

The teeth of the workpiece are ground (either from solid stock or following a preliminary rough forming or cut-' wheel is rotated about axis 29 and for this purpose assures J secured to a spindle 31, Fig. 3, journaled for rotation in a quill 32 which is axially slidable in a carrier 33 by means described hereinafter. The wheel is rotated by a motor (not shown) through a belt and pulley drive which includes pulley 34. The carrier 33 is pivoted by a pin 35 to a cradle 36 which is angularly adjustable through 360 about horizontal axis 37 in a cradle housing 38 rigid with frame 20, the cradle for this purpose being supported in the housing on axially spaced sets of roller bearings 39. A worm 41 journaled for rotation in cradle 36 meshes with a Worm gear segment 42 on the carrier 33. By turning this worm the carrier may be adjusted on the cradle about the axis of pin 35 to thereby offset the wheel axis 29 various distances from cradle axis 37; and, by rotating the cradle about axis 37, the direction of the offset may be varied as desired. By these two adjustments and those described in the preceding paragraph the wheel axis 29 may be brought into any desired relationship to the work axis 28, within the range of the machine.

The indexing mechanism on and within the work head 25 is shown schematically in Figs. 4, and 6. It comprises an electric motor 43 which through worm and wheel reduction gearing 44 drives a shaft 45 that is connected, by an electro-magnetic clutch 46, to a shaft 47 which is controlled by an electromagnetic brake 48. Through reduction gears 49 a shaft 51 carrying a cam 52 is driven at one-third the speed of shaft 47. On shaft 47 is the drive member 53 of an intermittent motion mechanism, this drive member carrying a roller 54. The driven member of the mechanism, 55, is splined to a shaft 56 for axial motion thereon, and it has two slots, 55' and 55", for periodically receiving the roller 54. Affixed to shaft 56 is a gearsegment 57 adapted to mesh intermittently with a pinionSSon shaft 47. The cam 52 on each revolution thereof acts th'rough a shifter lever 59 and a collar 61 aflixed on driven member 55 to shift back and forth on shaft 56 the driven member and a gear 62 which is affixed to it.

The index action is such that once every three turns of shaft 47, i.e. once for each turn of cam 52, the cam shifts the driven member 55 to bring the slots 55, 55" into the plane of roller 54. As the shaft 47 then rotates, counterclockwise in Figs. 5 and 6, the roller enters tangentially into the outer end of slot 55' (the position shown in Fig. 5) 'and accelerates the member 55 and shaft 56 from a standstill to a 'ma'ximum'velocity in a clockwise direction. At this instant (the positionshown in Fig. 6) the rollerleave's the inner end of slot 55', i.e. the end nearest the axis of shaft 56, and the pinion 58 makes driving contact with the first tooth of gear segment 57.

and 56. As the shaft 47 continues to rotate, the roller 54 passes through slot 55" and decelerates the member 55 to a standstill at the moment the roller departs from the outer end of the slot, this being a position of opposite hand to Fig.5. The cam 52 then acts to shift the assembly 55, 61, 62 to the position shown in Fig. 4,

wherein the slots on 55" are out of the plane 'of the roller, so that the driver 53, 54 turns idly. Th'e'intermittent motion mechanism comprising members 5 3, 54, '57 and 58 is essentially that of US. Patent No. 2,656,731,

granted October- 27, 1953, to E. Wildhaber.

The motor 43 runs at all times during normal operation of'the machine, but the clutch and brake units 46 and 48 are energized alternately so that the shaft 47 turns only intermittently,jwhen indexing is to take place. 'As will be seen'fromFigs. Sand 6, the actual indexing action,

from'the entry ofroller -54 into slot 55 until the departure of the roller from slot 55", occurs during one and onehalf turns of driver 53, and results in one complete turn of driven shaft 56. Therefore, of the three complete turns of shaft 47 per indexing cycle, one and one-half turns remain available for relative advance between the abrasive wheel and the workpiece following indexing, for the actual grinding operation and for the relative withdrawal between the wheel and the work which must precede the next indexing.

The intermittent indexing motion of shaft 56 is transmitted to the work spindle 27 through gear 62, a wide face pinion 63 which meshes with the gear 62, shaft 64, a set of change gears 65, shaft 66, worm 67 on the latter shaft and worm wheel 68 affixed to the work spindle. All of the shafts 45, 47, 51, 56, 64 and 66 are journaled for rotation in the work head 25. By selection of the change gears of the appropriate tooth number ratio the actual angle of indexing of the work spindle can be varied as desired, although the shaft 56 makes one complete turn during each index action. When indexing is not occurring the work spindle is positively held against rotation. This is accomplished in a usual manner by a spring backed lock dog, not shown, which engages a notch in a lock-up plate 69 on shaft 64. The lock dog may be of the general kind employed for the same purpose in the index mechanisms disclosed in Patent No. 2,188,996 to L. O. Carlsen and in Patent No. 2,477,105 to E. Wildhaber. A cam 71, co-rotatable with cam 52, acts to disengage the dog from the notch just prior to indexing and to allow it to re-engage at the conclusion of indexing.

The means for alternately effecting relative infeed and retraction of the grinding wheel and the work spindle, in time with the indexing action, are shown in Figs. 3, 4, 8 and -10. These means include a feed cam 72 mounted on 'aspindle 73 which is journaled for rotation in the -machine frame about vertical axis 74 and is driven by a variable speed reversible motor 75 through reduction gearing including worm and wormwheel 76. The cam acts against a follower roller 77 carried by cylinder 78 of a collapsiblestmt that is slidable within a guide 79 of the frame. The strut further comprises a piston 81 whose rod 82 abuts a pin 83 that is slidable in a bushing 84in the cradle 36. The pin abuts a lever 85 which is pivoted at 86 to the cradle and has its distal end bifurcated for pivotal connection at 87 to -a spool 88 which is slidableon pivot pin 35. A heavy coiled spring 89 acts-in compression between wheel spindle carrier 33 and thespool to urge the latter and the lever 85 to the left in Fig. 3, so that when the strut 78, 81 is extended, by

application of fluid pressure to the cylinder chamber to .the left of piston 81, the follower roller is held against feed cam 72 by spring pressure.

A cylinder 91 is slidable in the carrier 33 in a direction parallel to pin 35 and is' connected at 92 to the spool for movement as a unit therewith. Rod 93 of a piston 94 in thecylinder is screw-threaded to a non-rotatable nut 95 carried by the wheel-spindle-supporting quill 32. Normally piston 94 is held in its right position in cylinder 91, by hydraulic. pressure, so that rod 93 will abut a "in" or"cler to 'provide"stock'for dressing. Such advance is effected "by rotating the screw-threadedrod93 in nut 95, to thereby advance the quill and wheel assembly relative to the carrier 33 and screw 93. The screw is so rotated by movement of 'a' piston97fFig. 8, to the left in its cylinder 98,'the piston 'actirig 'througha known *r'atchet' mechanism, not "shown, but which includes a tightening clamp screws 135, Fig. l. grinding operation the forward position of the sliding ratchet wheel connected to the screw through a gear train including bevel gear 99, Fig. 3, shaft 101, gear 102, idler gear 103 on pin 35, and a gear 104 that is splined to rod 93 to permit relative axial motion of the rod. The ratchet mechanism may be of the kind shown for the same purpose in aforementioned Patent 2,395,544.

The strut 78, 81 is collapsed and extended by hydraulic fluid displaced by a pump unit operating in time with the index mechanism. This unit comprises a cylinder 105 having its opposite ends respectively connected by conduits 106 and 107 to opposite ends of strut cylinder 78, as shown schematically in Fig. 4. A piston 108 is reciprocated in cylinder 105 by a cam 109 secured to shaft 51, the cam having an endless cam path engaged by a follower roller 111 carried by the piston. The path of cam 109 is so shaped that preceding each indexing operation piston 108 is moved to the left in Fig. 4 to cause collapse of the strut 78, 81, and at the conclusion of indexing is moved to the right to cause extension of the strut. In practice the hydraulic circuit shown at 105, 106, 78, 107 includes means to keep it filled with fluid and to compel completion of each stroke of piston 81 relative to cylinder 78, this being in accordance with patent application Serial No. 595,255, filed July 2, 1956, by L. O. Carlsen et a1., entitled Hydraulic Motion Transmitting System, now Patent No. 2,882,685, dated April 21, 1959.

The position of the sliding base 21 along the ways 22', Fig. 1, is controlled by the mechanism shown in Fig. 9.

.This mechanism includes a screw 112 rotatable in a bracket 113 secured to frame 20. The screw is connected through bevel gears 114 to a shaft 115 which is 'adapted to be turned by a socket wrench and which carries a calibrated dial 116. The screw 112 is threaded .to a non-rotatable nut 117 on a slide 118 which is movable on the frame along ways 22 and comprises a cylinder in which a piston 119 is reciprocable by hydraulic pressure. The piston is connected by piston rod 121 and by a bracket 122 to the sliding base 21. Rotatable in the slide 118 is a shaft 123 carrying a position-indicating dial 124, a ratchet wheel 125, and a variable stop drum 126, the right face of the latter having a plurality of circularly arranged and relatively stepped stop surfaces 127. The height of the steps is exaggerated in the drawings, and in practice there are five steps respectively of eight, eight, eight, four and two thousandths of an inch, each step representing the amount of infeed of the work C relative to the wheel W between successive grinding passes during the finish grinding cycle.

A bar 128 abuts one of the stop surfaces 127 for the purpose of limiting advance of the sliding base 21, i .e. motion of the sliding base to the left in Fig. 9 effected by piston 119. The bar is slidably supported by slide 118 and is adapted to abut one of a plurality of circularly arranged and relatively stepped stop surfaces 129 on a .disc 131 that is rotatable in bracket 122. The disc is .erably on the order of five ten-thousandths of an inch (0.0005"). Hence by turning the knob, at a time when the piston 119 has Withdrawn the sliding base, the machine operator may make fine adjustments of the advanced positionof the sliding base, without disturbing .the adjustment made by turning shaft 115. The knob ,is, held in adjusted position by a springbacked detent 134. The adjustment of the slide 118, by turning shaft ,115, is made during set-up of the machine and after it is made the slide 118 is clamped to the frame 20 by During the finish base issuccessively advanced by step-by-step turning of the stop drum 126 by an automatic mechanism which functions when the sliding base is withdrawn by piston 119. Upon such withdrawal a spring 136 acts against a pin 137 on the bar 128 to move the bar from abutment with the stop drum to permit the latter to be turned. This motion of the bar is limited by abutment of pin 137 with a part 138 of the slide 118 so that withdrawal of the sliding base separates the stop disc 131 from bar 128, thus enabling the stop disc to also be turned.

The mechanism for automatically turning the ratchet wheel and stop drum 126 is essentially like that disclosed in aforementioned Patent 2,395,544. It comprises a piston 139 engaging a pin 141 carried by a rocker 142 angularly movable on shaft 123, and a pawl 143 carried by the rocker and engaging the ratchet wheel. Upon each stroke of piston 139, to the right in Fig. 8, the ratchet wheel is advanced by one tooth and the stop drum by one step. During the return stroke of the piston the stop drum assembly is held against retrogression by a friction brake 144. Upon completion of the finish grinding cycle the pawl 143 is released by motion, to the left in Fig. 8, of a piston 145; and the stop drum assembly is returned to its initial position by motion to the left of a piston 146 which, as indicated in Fig. 9, has rack teeth engaging gear teeth 147 on shaft 123. The initial position of the stopdrum assembly is adjustable by means of a screw 148, Fig. 8, which limits the stroke of piston 146. By this adjustment any desired number of the steps provided on stop drum 126 may be utilized in finish grinding.

The wheel W is periodically dressed by automatic dressers, not shown, but which may be similar to those disclosed in aforementioned Patent 2,395,544. Their operation is controlled by a known type of motor operated control unit, similar to that shown in Fig. 18 of the patent. This unit, designated 149, Figs. 1 and 13, when electrically energized performs the following functions in sequence: 1) opens a normally closed switch 151 to cause withdrawal of sliding base 21 and retraction of wheel W by piston 94; (2) operates a valve 152, Fig. 8, to cause advance and then retraction of wheel feed piston 97; (3) closes switch 151 to cause return, i.e. advance of the sliding base and of wheel-shifting piston 94; (4) causes the automatic dressers to operate through their cycle; (5) closes a normally open switch 153 to start the indexing function; (6) closes momentarily a normally open relay-control switch 154; and (7) opens momentarily a normally closed switch 155 which stops its drive motor, thus concluding the dressing cycle.

The reversible variable speed motor 75 for feed cam '72 is controlled by four separate electro-magnetic' controllers designated on Figs. 13 as RF (roughing feed), RR (roughing return), FF (finishing feed) and FR (finishing return). These controllers in turn are governed by several instrumentalities including normally open limit switches 156, 157 and 158, appearing in Figs. 10, 11 and 12. Switch 156, which has two contacts 156a and 156b, Fig. 13, is closed by a cam 159 (see also Fig. 3) on shaft 73 only when the high or zero position of cam 72 contacts follower 77, this being the position shown in Figs.

4 and 11. Switch 157 is closed only when its actuating arm is contacted by a stop 161 carried by cam 72. This is the position shown in Fig. 10. Stop 161 is adjustable on the cam and may be set at various angular distances from the zero position of the cam, depending upon the amount of roughing feed motion that is desired. To enable such adjustment the stop 161 is held by a bolt 162 and knurled nut, the bolt head being engaged in an annular T-slot 163 in the cam. Switch 158 is closed only when its actuating arm is contacted by a stop 164 which is fixed to the cam, this being the position shown'in Fig.

the cam 72 slowly, in a clockwise direction, until the position shown in Fig. 11 is reached, this being the position' in which switch 156 is closed. This closure results in the 'controller RR being energized to cause the feed motor to rapidly return the cam, counterclockwise, to the roughing feed'staiting position, Fig. 10. During the clockwise feed motion the cam slowly moves the follower roller 77 to the right, thereby feeding the grinding wheel W into the tooth space of the workpiece. As shown in Fig. 10 the roughing feed path of the cam, from roughing 'start point R to the high point 0, comprises a plurality of discrete infeed sections 165, all of which constitute spirals of gradually increasing radius from axis 74. These infeed sections'are separated by depressions 166 which constitute retraction sections which allow a slight motion of the follower 77 and wheel W to the left (under the urge of spring 89, Fig. 3) sufiicient to interrupt the grinding 'operationand to allow the entryof coolant between the 'wheel and the surfaces being ground.

During the finish grinding operation, when switch 158 is closed by stop 164, this being the condition shown in Fig. 12, the controller FF is energized and causes motor 75 to rotate the cam 72 counterclockwise. During this operation the wheel is fed quickly into full finishing depth, without interruption, the finishing path F to O of the cam being a spiral of continuously increasing radius. At the moment the high point of the cam contacts the follower 77, the position of Fig. 11, the switch 156 is closed and energizes the controller PR to cause a rapid return of the cam, clockwise to the position of Fig. 12.

Each of the controllers RF, RR, FF and FR is independently adjustable to vary the speed of the motor 75 so that the roughing feed, the finishing feed, and the return feed motions each can be effected at the desired rate. Tooth-to-tooth indexing of the work takes place during the return feed motions and the latter are so timed as to be concluded slightly before the indexing is completed.

With reference to Fig. 8, the control system further includes a sump 165 for hydraulic fluid, and a pump P for pumping the fluid through line 166 to various pressure operated devices from which-it returns through line 167 to the sump. A manually operated reversing valve 168 connected across lines 166 and 167 controls a cylinder-piston unit 169 whose piston is moved to the right to chuck the work to the work spindle of the machine, and to the left for dechucking. At the same time that dechucking occurs, through application of pressure to line 171, pistons 145 and 146 are moved to the right to release the ratchet pawl 143 and reset the variable stop drum to its lowest surface 127 upon which bar 123 rests during the rough grinding operation. A valve 172 is controlled by solenoids 173 and 174. Following energization of solenoid 73 this valve applies pressure through line 175 to move to the right the piston of unit 176 (comprising cylinder 118 and piston 119), for withdrawing the sliding base 21, and to move piston 139 to the right to advance the variable stop drum. Following energization of solenoid 174 the valve applies pressure through line 177 to advance the sliding base and reset the piston 139. Another valve 178, called the blocking valve, is controlled by solenoids 179 and 181. Upon energization of solenoid 179 it is closed to block flow from line 175 against piston 139; and upon energization of solenoid 181 it is opened to permit such flow. A valve 182 controls the position of piston 94 in cylinder 91, Fig. 3. Upon withdrawal of sliding base 21 the valve 182 is operated to cause movement of piston 94 to the left, to retract wheel W. Upon advance of the sliding basethe valve'is operated by a spring 183 to cause the piston-to move to the right to advance the wheel.

- Referring to Fig. 13, the control system further includes a pair of electricleads' Ll and L2, and, connectible across these leads, a controller WC for the drive motor for wheel W,'the controller having contacts WC-l which'are closed only when the controller is energized; a holding r'elay -1R having contacts lR-l closed only when the relay is energized; the feed motor controllers RF, FR,

RR and FF,:includingcontacts-RF-Land FF-l closed I' enemies only when their respective controllers'RF and FFiare energized; the dresser control unit 149 and the switches 151, 153, 154 and operated by it; a dresser control latch relay 2R which is put out when its winding 2R- OUT is energized and in when its winding 2R-IN is energized, this relay having contacts ZR-l and 2R-2 which are closed only when the relay is out and contacts 2R-3 and 2R-4 which are closed only when it is in; a relay 3R for controlling solenoids 173 and 174, and having contacts 3R-1 and 3R2 closed only when the relay is energized and contacts 3R-3 closed only when it is deenergized; a rough-finish selector latch relay 4R having an out winding 4R-OUT and in windings 4R-IN, nine sets of contacts 4R-1 through 4R-9 which are closed only when the relay is out and seven sets of contacts 4R- 10 through 4R-16 closed only when it is in; a latch relay 5R for activating feed cam switch 156, having in winding 5R-IN, an out winding 5R-OUT, and contacts 5R-1 closed only when the relay is in; a feed motor control latch relay 6R having in and ou windings 6R-IN and R-OUT, contacts 6R-1 closed only when the relay is in and contacts 6R-2 and 6R-3 closed only when it is out; and a latch relay 7R with in and out windings 7R-IN and 7R-OUT, and contacts 7R-1 and 7R-2 closed and opened respectively only when the relay is in and out, for controlling the electro-magnetic clutch 46 and the brake 48 of the index mechanism.

The control system shown in Fig. 13 further includes two conventional electricallyoperated counters, IT and 2T, which are actuated upon each closing of a switch 184. This switch is momentarily closed by a cam 185 on index cam shaft 51, once upon each revolution of the latter. Counter IT is adjustable for the total number of teeth in the workpiece, and upon receiving a corresponding number of energizations by closing of switch 184 it resets itself and momentarily opens its contacts IT-l and closes its contacts 1T-2. Similarly counter 2T is adjustable for a number of rough grinding cycles to precede each dressing operation. For example if the wheel is to be dressed after roughing grinding seven teeth, the counter is so adjusted that after upon every seventh energization it automatically resets itself and momentarily closes its contacts 2T-l and 2T-2.

Two other limit switches, 186 and 187, are operated respectively by cams 188 and 189 aflixed to index cam shaft 51. Switch 187 has two sets of contacts designated 187a and 18717. The relationship of switches 184, 186 and 187 (and of their actuating cams 185, 188 and 189) to the indexing cycle, i.e. to a complete revolution of cam shaft 51, is shown in diagram Fig. 7. There position 191 represents the beginning of the actual indexing, 192 the end of actual indexing, and 193 the end of the indexing cycle. Cam 52 shifts the Geneva driven member 55 out of operative relation to the driver 53, 54 between positions 194 and 195 and back into operative relation between positions 196 and 197. Cam 109 acts to collapse the strut 78, 81, between positions 198 and 199, to retract the wheel W to permit indexing of the work, and acts to extend the strut between positions 192 and 261. Switch 187 is closed, to enable starting ofthe grinding operation, immediately after position 201 in which the wheel W is brought forward by extension of strut 78, 81 at the conclusion of actual indexing. Switch 186 is closed immediately before position 198'where'the wheel retraction is begun in preparation for the indexing operation, to cause the index cycle to await completion of the grinding operation. Switch 184 closes at position 199, slightly before the index cycle end position 193.

Still other control instrumentalities include push button type "start and stop switches 202 and 203, Fig. 13,

"for the wheel motor controller WC; similarstart and'stop 1switches'2ii4 and 205 Zfor'the feed motor controllers; and

three limit-switches, .206, 207' and 208,- associated "with the variable'stop'drum 126, Fig. 9. Switch 206 has three contacts of'which 206a is-- normally closed and 206b an'd aesaiea 9 206a are normally open. A button 209 on the drum actuates the switch to open contact 206a andclose contacts 20Gb and 2060 upon the final advance of the drum made after conclusion of finish grinding. Normally open switch 207 is closed by the engagement therewith of pawl 143 upon the completion of each advance of the stop drum. Normally open switch 208 is momentarily closed, to start wheel dressing cycles, by buttons 211 on the drum as these buttons pass under the switch during the advance of the drum effected by piston 139 and pawl 143. In setting the machine up for operation the buttons 211 are inserted in various openings provided for them in the drum to determine when wheel dressing will occur.

After the machine has been set up and a workpiece placed on spindle 27, operation is commenced by manually operating valve 168 to move the piston of unit 169 to the right to effect chucking. Then the wheel motor controller WC is energized by momentarily closing wheel start switch 202 since at this time the final stop switch contact 206a is closed. Similarly feed control relay IR is energized by momentarily closing the feed start switch 204. Upon energization of the wheel motor controller the contact WC-l closes to maintain the circuit upon reopening of the switch 202, and, since relay contact 2R-3 is closed at this time, the dresser control unit 149 is energized to eifect the dressing cycle.

In the dressing cycle, the unit 149 opens switch 151 to deenergize relay 3R whereupon contacts 3R-3 close and energize the valve operating solenoid 173 to cause sliding base 21 to be withdrawn; and upon such withdrawal control valve 182 is operated to move piston 94 to the left to retract the wheel to its dressing position (the strut 78, 81 being collapsed at this time). The unit 149 then operates a valve 152, Fig. 8, to cause the wheel feed stroke and subsequently the reset stroke of piston 97; operates the wheel dressers through one cycle; then recloses switch 151 to energize relay 3R and thereby closing contact 3R-2 to energize solenoid 174 and thus effect advance of the sliding base, and also movement of piston 94 to the right to thereby advance the wheel; then closes switch 153 to put in latch relay 7R; opens switch 154 to put out latch relay 2R (so that contacts 2R-3 for the dresser control open); and finally opens momentarily the normally closed switch 155,whereupon unit 149 stops. While the first cycle of the unit 149 is occurring the feed motor 75 is operated by energization of controller RR through the circuit including now closed contacts 1R-1, 6R-2, 4R-3, and 4R-2. Contacts 1R-1 are closed immediately upon energization of winding 1R. Contacts 6R-2 are closed by a momentary energization of 6R-OUT when the feed start switch is closed (through the circuit including 5R-1 and 4R-7). However this momentary energization also puts out latch relay 5R, so that contacts 5R-1 open. When the feed cam 72 reaches its roughing return limit position, switch 157 is closed, thereby putting in the relay 6R. This opens contacts 6R2 to stop the feed motor.

When at the conclusion of the actual dressing operation the dresser control unit 149 closes switch 153, index controller 7R is put in, and the index mechanism is operated through to position 198, Fig. 7. As it passes through position 201 the switch 187 is closed. This establishes a circuit through now closed contacts 6R-1, contact 187a and controller RF to operate the feed motor through the roughing feed cycle. Although switch 187 is only momentarily closed the contacts RF-1 close to hold the controller circuit energized. The roughing feed cycle ends when the feed cam closes switch contact 156a to put latch relay 6R out and thus open contacts ,6R-1. When index position 198 is approached the index stops because switch 186 is momentarily closed to. put latch relay 7R out. The index is not restarted until the grinding operation is completed, this being when switch 156 is closed. Contact 15Gb of this switch then puts in 10 relay 7R; since contacts 2R-2'are closed at this time: and therefore the index operates through another cycle. Meanwhile the closing of switch contact 156a has put out latch relay 6R so that the roughing return feed is started by establishment of the circuit through contacts 6R-2, 4R-3, 4R-2 and controller RR. At the conclusion of this return feed, switch 157 closes, thereby putting in latch relay 6R, and this is followed by closing of the index switch 187 which starts another roughing feed.

Thus alternate indexing and roughing grinding of the work will take place. Preceding each indexing operation the wheel will be withdrawn (beginning at position 198 of the index cycle) by collapse of strut 78, 81 and after such indexing (beginning at position 192 of the cycle) the strut is again extended. During each indexing cycle, at position 199, the switch 184 momentarily closes to energize the counters IT and 2T. When counter 2T counts out, after the rough grinding of the, particular number of teeth for which it is set, then upon the closing of switch 184 the counter immediately closes momentarily its contacts 2T-1 and 2T-2. Closing of 2T-2 puts out controller 7R, thereby opening contacts 7R-1 and closing 7R7-2 and so stopping the index. Closing of 2T-1 puts in relay 2R, whereupon closing of contacts 2R-3 starts the dressing control unit 149, which operates through the same sequence, described above. During the conclusion of this sequence the indexing and rough grinding operations result from closing of switch 153.

When the counter 1T counts out, as a result of allof the teeth having been rough ground, the switch 1T-2 closes. This puts in selector latch relay 4R, and through closing of contacts 4R13 also puts in latch relay 5R. Closing of contacts 4R-16 energizes solenoid 181, opening the blocking valve 178; opening of contacts 4R-6 and 4R-7, and closing of contacts 4R-14 and 4R-15 changes the function of switch contact 156a with respect to the direction of feed motion of cam 72, and de-activates switch 157 while activating switch 158; and opening of contacts 4R-8 renders counter 2T inactive. Closing of contacts SR-l puts in relay 6R, and thereby starts the finish return feed through closing of the circuit through contacts 6R-1, 4R-10 and 4R-11 and controller FR. This return feed continues until feed cam operated switch 158 closes, putting out relay 6R. This opens contacts 6R-1, deenergizing controller FR, and also closes contacts 6R-3 putting out relay SR and opening its contacts 5R-1.

Meanwhile the opening of switch contacts lT-l has deenergized relay 3R. Thereupon contacts 3R-3 close, energizing the solenoid 173 to begin withdrawal of the sliding base 21 and advance of the variable stop drum (piston 139) to the first finishing grinding step 127. A dressing button 211 at this time closes dress selector switch 208. This puts relay 2R in and starts the dresser control unit 149, which thereupon carriesout the same sequence of operations above described, at whose conclusion the switch 153 is closed. During this sequence, when the sliding base is advanced the variable stop piston 139 is simultaneously reset, i.e. moved to the left in Fig. 8.

Closing of switch 153 puts in index controller 7R, so that index mechanism operates through to position 198, Fig. 7. At position 201 switch contact 187b is closed, and since contacts 6R-2 and 4R-12 are now closed, the controller FF is energized and a finishing feed operation takes place. Although switch contact 18712 is closed only momentarily the circuit of controller FF is held by closing of its contacts FF-l. At the conclusion of the finishing feed, the feed cam operated switch 156 closes, putting in relay 6R. This opens contacts 6R-2 to deenergize controller FF and closes 6R-1 to close the circuit through contacts 4R-10 and 4R-11 and controller FR to start the finishing return. At the same time the closing of contact 156b puts in relay 7R, since contacts 2R2 are now closed; and this starts another indexing cycle. -r

'A*series of alternateindexing and finish grinding op erations take place in the manner just described until all the teeth around the workpiece have been subjected to the first finish grinding operation. contacts 1T-1 are momentarily opened and, as before, -deenergizes the relay 3R to cause retraction of the sliding base and advance of the variable stop drum to'the Then the counter next step. Only a slight retraction'takes place because as soon as the variable stop drum advances, the pawl switch 207 is closed, energizing relay 3R (since contacts 2R-1 are now closed) and thereby causes the sliding base to return to its advanced position and the variable stop piston 139 to be reset.

The advance of the variable stop drum as described in the preceding paragraph does not interrupt the alternating indexing and finish grinding operations, which continue unless and until an advance of the variable stop drum brings a dress selector button 211 into contact with switch 208. In that event the relay 2R is put in, thereby again starting the dresser control unit 149. The resulting sequence of dressing operations is followed by a further series of indexing and finish grinding operations.

After the last finish grinding operation the ensuing .ad- Vance of the variable stop drum brings the final stop button 209 beneath the switch 206, thereby to (a) open contact 206a and deenergize the circuits of the wheel motor controller WC and the feed control relay 1R, and opening their holding contacts WC-l and lR-l, with the result that the feed motor controllers and the dresser control unit 149 are all inactivated; (b) close contact 2060 to put out the relay 4R; and (c) close contact Gb put in the latch relay 2R. This latter, by closing of contacts 211-3, conditions the dresser control unit 149 for operation as soon as the start switches 202 and 204 are manually closed the next time. The opening of contact 206a also deenergizes the relay 3R, causing its holding contacts 3R-1 to open and its contacts 3R-3 to close,

thereby energizing the valve-operating solenoid 173 and causing withdrawal of the sliding base. By manual operation of valve 168 the operator may now apply pres sure to line 171, causing actuation of unit 169 to dechuck the work and actuation of pistons 145 and 146 to release the ratchet pawl 143 and reset the variable 'stop drum. This resetting closes switch contact 206a and opens contacts 20Gb and 2060, all however without immediate effect. One complete operating cycle is now concluded and the machine is ready for the next such cycle as soon as the finished workpiece is removed and afresh blank is placed on the work spindle.

From the foregoing it will be understood that the selector relay 4R, and relays SR and GR, acting in conjunction with the counter 1T, the switches 156, 157 and 158 and the four feed motor controllers, constitute a shifting mechanism to render effective one or the other of the two feed paths R to O and F to O of the feed cam '72; and that the valve 178 controlled by this mechanism constitutes a means for blocking and unblocking the variable stop drum 126, so that the rough grinding of each tooth is completed before indexing to the next, whereas the finish grinding is carried out by the conventional prior method in which the work is indexed around a plurality of times, with only a small amount of stock being removed for each indexing.

In the modification shown in Figs. 14 through 19, the principal difierences over the machine described hereinbefore reside in the substitution of a constant speed, nonreversing feed cam motor 212 for the feed motor 75; the

substitution for the oscillating feed cam 72 of aunidi- .rectionally rotating cam comprises one section 213 for effecting the roughing feed and return motions of wheel Wr-and another and separate section 214 for-effecting the "finishing feed and return motions of the wheel; and the substitution, for the electrical shifting mechanism for selecting the'roughing and finishing cam feedpaths, of a hydraulic-mechanical shifting mechanism. This mechanism comprises an angularly movable carrier 215 for bringing a cam'follower 216 carried thereby into operative relation to either the roughing'feed carn section 213 or the finishing feed cam section 214, thereby rendering one or the other of these sections effective.

As shown in the drive diagram, Fig. 18, the motor 212 drives the feed cam 213, 214 through a drive train comprising bevel gears 217 and 218, shafts 219 and 220 which are connected by certain coupling and gearing means, bevel gears 221, shaft 222, bevel pinion and gear 223 and 224, shaft 225, bevel gears 226, and the shaft 227 which carries the cam 213, 214. For rough grinding, the shaft 219 is connected to shaft 220 for driving the latter at relatively low speed through speed change gears 228, shaft 229, pinion 231, idler gear 232, gear .233, and electro-magnetic coupling 234; while for finishing grinding the shaft 220 is driven at relatively high speed through speed change gears 235, shaft 236 and electro-magnetic coupling 237.

Referring to Figs. 15 and 16, when the zenith or 0 point of feed cam section 213 or 214 is in contact with follower 216, the single lobe of a cam 238 on shaft 227 contacts and closes a normally open limit switch 156, which is employed (instead of the switch contact 156b of the first embodiment) to start the indexing operation. Indexing takes place while the cam is turning clockwise to the position thereof in which the low point, designated R in Fig. 15 and F in Fig. 16, contacts follower 216. The speed change gears 228 and 235, Fig. 18, are selected by the machine operator in view of the particular cam sections 213, 214 being used, so that this low-point position will not be reached until after indexing i completed, enabling operation of the motor 212 to be continuous except when wheel dressing occurs. The feed path of cam section 213 is periodically interrupted by grindingrelief depressions 239, corresponding in function to depressions 166 in Fig. 10.

The carrier 215 for follower roller 216 is rotatable in guide 79 but otherwise is similar in function to part 78 which it replaces, it being the cylinder of a collapsible strut assembly which includes the piston 81. The carrier has gear teeth 241 thereon engaged by rack teeth on a piston 242, to oscillate the carrier through between the respective positions thereof in which the roller engages one or the other of the cam sections 213 and 214.

Fig. 17 shows only that part of the complete hydraulic system which is different from the system shown in Fig. 8, this being the part controlled by solenoids 179, 181. In Fig. 17, these solenoids designated 179, 181 control a reversing valve 243 which is connected across pressure and return lines 166 and 167 of the hydraulic system. This valve controls the position of piston 242 and also that of a piston 244 which operates a reversing valve 178. This valve 178' replaces valve 178 of Fig. 8 and is employed for the same purpose, namely to block or unblock the hydraulic circuit for the variable stop drum advancing piston 139. When solenoid 179 is energized the follower roller 216 is engaged with roughing cam section 213 and the hydraulic circuit for piston 139 is blocked; and when solenoid 181' is energized the follower roller 216 is shifted to engage the finishing cam section 214 and the hydraulic circuit for'piston 139 is unblocked.

The electrical system shown in Fig. 19 is much like that of Fig. 13 and, for ease of reference, only the elements which are different are shown by heavy reference numerals in Fig. 19. The differences in arrangementand operation are as follows: The controllers RF, FR, RR

and FF and the circuits therefor between contacts 1R-1 and line L-2 are replaced by a controller PC for the feed motor 212 and, in parallel with the controller, the windings of the electro-magnetic couplings 234 and 237. In series with controller PC are contacts 2R-5 of latch relay 2R, which contacts are closed only when the relay is out, and switch 187' which replaces switch 187 of the first embodiment. .Shunting switch .187 are holding con- 13 tacts FCXI which are closed only when the controller PC is energized. In series with coupling 233 are contacts 4R-17 of latch relay 4R, which contacts are closed only when this relay is out; while in series with coupling 234 are other contacts 4R-18, of the same relay, which are closed only when the relay is in.

The operating sequence is similar to that first described. After the first dressing and indexing operations the switch 187 closes momentarily, and, contacts 2R5 being closed at this time, the controller PC i energized and is held energized by closing or" its contacts FC-l, so that feed motor 212 operates. Since at this time contacts 4R-17 are closed, the coupling 234 is energized and hence the earn 213, 214 is rotated at low speed. Contacts 4R-9 also being closed at thi time, the solenoid 179' is energized with the result that roller 216 is on roughing cam section 213. When the roughing feed has brought'the wheel W to full roughing depth the cam 238 closes switch 156', thereby putting in latch relay 7R and causing the indexing operation which is completed by the time the feed cam has rotated far enough to bring point R thereof beneath roller 216. Indexing followed by rough grinding continues without interruption until rough dress counter 2T counts out, this, as before, putting in latch relay 2R, which stops the feed motor 212 by opening contacts 2R-5, and, also as in the first embodiment, causes the wheel dressing operation to occur. At the conclusion of dressing the indexing operation resumes, and is followed as before by rough grinding.

When the teeth have all been rough ground, the counter 1T acts, as in the first embodiment, to put in relay 4R. By the resulting deenergization of solenoid 17W and energization of solenoid 181' the follower roller 216 is shifted to the finishing section 214 of the feed cam, and the blocking valve 178 is opened, allowing the piston 139 to advance the variable stop drum to the first finishing step. As before, this results in another wheel dressing operation at whose outset the feed motor i stopped by opening of contacts 2R-5. Also, by reason of relay 4R being put in, contacts 4R-17 open and 4R-18 close, so that magnetic coupling 234 is deenergized and coupling 237 energized. Consequently, after the dressing and indexing operations, when the contacts 2R-5 and then the switch 187' close to again energize the controller PC, the motor operates the feed cam at the higher speed. Just as in the preceding roughing operation, the cycle of indexing followed by grinding continues without interruption except that occasioned by dressing, until the finish grinding is concluded, as in the first embodiment, by opening of final stop switch 206 by the button 209.

Having now described the preferred embodiments of our invention, and the operation thereof, what we claim 1s:

1. A tooth grinding machine comprising a grinding wheel and a work spindle, means including a feed cam for eflfecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle between successive infeed motions, said feed cam having a roughing feed path and a finishing feed path, and a shifting mechanism to render elfective one or the other of said feed paths, further means for periodically effecting relative withdrawal and advance motions between the grinding wheel and the work spindle, a variable stop to limit such relative advance motions between the wheel and spindle, actuating means operable concomitantly with such relative withdrawals for advancing the variable stop to successive stop positions, and blocking means for preventing such advance of the variable stop while the roughing feed path of the feed cam is effective.

2. A tooth grinding machine comprising a grinding wheel and a work spindle, means including a feed cam for effecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle betweensuccessive infeed motions, said feed cam having a roughing feed path and a finishing feed path, and a shifting mechanism to render effective one or the other of said feed paths, said shifting mechanism being arranged to render said finishing feed path effective after a selected number of cycles of indexing and infeed by the roughing path, the roughing feed path of the cam comprising a plurality of discrete infeed sections separated by retraction sections, so thatwhile the roughing feed path is effective the wheel and the work are periodically separated.

'3. A tooth grinding machine comprising agrinding wheel and a work spindle, means including a feed cam for efiecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle between successive infeed motions, said feed cam having a roughing feed path and a finishing feed path, and a shifting mechanism to render effective one or the other of said feed paths, and a reversing motor for oscillating the feed cam.

4. A machine according to claim 2 in which said'motor is of the variable speed type whereby the rate of infeed effected by the feed cam may be varied, and means for causing the motor to operate at difierent speed when the finishing cam track is effective than when the roughing cam track is eifective. a 5; A machine according to claim 2 in which there is one control for operating the motor when the roughing feed path is effective and another control for operating the motor when the finishing feed path is efiective, whereby the roughing and finishing feeds may be effected at different motor speeds.

6. A machine according to claim 2 in which the roughing feed path and the finishing feed path are both provided on the same cam unit, and the shifting mechanism comprises the control system for said reversing motor whereby said cam unit is operated through one angle for roughing and through another angle for finishing.

7. A machine according to claim 5 in which the roughing and finishing feed paths have a common zenith at which the relative infeed between the wheel and the workpiece is maximum, and the reversing motor effects the infeed by driving the cam in one direction while said roughing feed path is effective and by driving the cam in the opposite direction while said finishing feed path is effective.

8. A tooth grinding machine comprising a grinding wheel and a work spindle, means including a feed cam for effecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle between successive infeed motions, and a collapsible strut for transmitting from the feed cam the relative infeed motion between the wheel and the work spindle, and control means for the strut, operating in time with said cam means, for effecting collapse of the strut at the conclusion of such relative infeed and for effecting extension of the strut prior to such relative infeed.

9. A machine according to claim 7 in which there is a resilient means acting to urge the relative withdrawal motion between the wheel and the work spindle upon collapse of said strut.

10. A machine according to claim 7 in which there is a means for effecting operation of the indexing mechanism during the return motion effected by the feed cam, and in which said strut control means comprises a hydraulic piston-cylinder device operated by said indexing mechamsm.

'11. In a tooth grinding machine or the like, a feed mechanism comprising a rotary cam having roughing and finishing feed paths, a reversible motor for oscillating said cam, and control means for the motor including switch means responsive to angular motion of the cam for effecting reversal of the motor, said switchmeans being adjustable to vary the angle of effective motion of one of said feed paths.

12. A mechanism according to claim 10 in which there is a cam follower engaging said cam and in which said control means includes a selector to cause the motor to oscillate the cam through an angle in which the roughing path engages the follower or through another angle in which the finishing path engages the follower.

13. Amechanism according to claim 10 in which there is a cam follower roller engageable with said cam, 21 collapsible strut arranged for reciprocation and connected to the follower roller for movement thereby, and strut control means operating in time with the cam for collapsing the strut at the conclusion of one stroke of the follower and extending it at the conclusion of the return stroke of the follower.

14. A tooth grinding machine comprising a grinding wheel and a work spindle, means including a feed cam for effecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle between successive infeed motions, said feed earn having a roughing feed path and a finishing feed path, and a shifting mechanism to render efiective one or the other of said feed paths, said shifting mechanism being arranged to render said finishing feed path effective after a selected number of cycles of indexing and infeed by the roughing path, a variable stop to limit the depth of grinding engagement between the grinding wheel and work on the work spindle, and means for holding said stop against advance while the roughing feed path is effective and for advancing said stop while the finishing feed path is efiective and in response to the occurrence of said selected number of operations of the indexing mechamsm.

15. A tooth grinding machine comprising a grinding wheel and a work spindle, means including a feed cam for effecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle between successive infeed motions, said feed cam having a roughing feed path and a finishing feed path, the roughing feed path comprising a plurality of discrete infeed sections separated by retraction sections, so that while the roughing feed path is effective the wheel and the work are periodically separated, and a shifting mechanism'to render one or the other of said feed paths effective.

16. A tooth grinding machine comprising a grinding wheel and a work spindle, means including a feed cam for effecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle between successive infeed motions, said feed cam having a roughing feed path and a finishing feed path, means torender one or the other of said feed paths efiective, a variable stop to limit the depth of grinding engagement between the grinding wheel and work on the work spindle, and means for holding said stop against advance while the roughing feed path is effective and for advancing said stop while the finishing feed path is effective.

17. A tooth grinding machine comprising a grinding wheel and a work spindle, means including a unidirectionally rotatable feed cam for efiecting alternate relative infeed and return motions between the Wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle between successive infeed motions, the rough and finish feed paths of the cam each having an infeed portion and a return portion, the infeed portion of the roughing cam comprising a plurality of discrete infeed sections separated by retraction sections, so that while the roughing feedpath is effective the wheel and the work are periodically separated, and a shifting mechanism to render one or the other of said feed paths effective.

18. A tooth grinding machine comprising a grinding wheel and a work spindle, means including a unidirectionally rotatable feed cam for effecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a workpiece on the spindle and for returning for a subsequent infeed, a mechanism for angularly indexing the work spindle between successive infeed motions, the rough and finish feed paths of the cam each having an infeed portion and a return portion, means to render one or the other of said feed paths efiective, a variable stop to limit the depth of grinding engagement between the grinding wheel and work on the work spindle, and means for holding said stop against advance while the roughing feed path is effective and for advancing said stop while the finishing feed path is efiective.

19. A tooth grinding machine comprising a grinding wheel and a work spindle, means including a rotary feed cam for effecting alternate relative infeed and return motions between the wheel and the spindle, respectively for grinding a tooth surface of a workpiece on the spindle and for returning for a subsequent infeed, and means for angularly indexing the work spindle between successive infeed motions, the infeed portion of said cam comprising a plurality of discrete infeed sections separated by retraction sections, so that while the infeed is occurring the wheel and the tooth surface being ground are periodically separated.

References Cited in the file of this patent UNITED STATES PATENTS 2,099,674 Bullock et a1. Nov. 23, 1937 

